Automatic safety switch for induction motors



Dec. 1a, 192& 1,695.866

e. SP EISER AUTOMATIC SAFETY SWITCH FOR zunucno n MOTORS Filed Aug. 1, 1925 4 NV E NTO R GOIY/IPb .ajoe/ser W ATTORNEY a low-voltage relay. The starting relay re-.

Patented Dec. 18, 1928.

UNITED STATES PATENT OFFICE.

GOTTLIEB SPEISEB, OF NUREMBE RG, GERMANY, ASSIGNOR TO WESTINGHOUSE ELEC- TRIO & MANUFACTURING COMPANY, OF NEW YORK, N. Y., A CORPORATION.

AUTOMATIC SAFETY SWITCH FOR INDUCTION MOTORS Application filed August 1, 1925, Serial No. 47,611. and in Germany February 5, 1924. v

My invention relates to improvements-in automatic safety switches for induction motors.

An automatic safety switch for induction motors is already known on the tripping mechanism of WlllCh act three different relays viz: a startingrelay, an overload relay and sponds to a heavy current, such as occurs when the normal starting current exceeded, the overload relay when the normal operating current is exceeded and the lowvoltage rela when the network voltage drops or falls. hile the starting relay and the low-voltage relay act directly upon the tripping mechanism of the switch, the overload relay controls a thermostat which trips the switch after a certain delay by means of the low-voltage relay.

The object of my invention is to reduce .the number of relays required while maintaining substantially the same manner of operation of the switch.

According to my invention the switch con-- trolling the thermostat to obtain delayed tripping is associated with the overload relay and the path of the relay armature is extended beyond the point of engagement with: the thermostat controlling switch into the tripping, mechanism of the safety switch for the purpose of being able to utilize the overload relay at the Sametime as a starting relay by causing immediate tripping upon heavy overloads. v

i;In the drawing affixed to this specification and forming a part thereof, the improved safety switch is shown diagrammatically. The switch differs from the usual construction in the arrangement and the construction of the relay.

Like parts are indicated: by like letters and numbers of reference in the various elements of the system.

Referring to the drawing it will be seen that in the lines of the automatic switches 'A A A are connected the three release magnets F F,, F,. The tripping mechanism of the automatic switch A is furthermore subjected to the action of a low-voltage relay G ofknown construction. The tripping ma net F combines in itself the starting relay 'and the overload relay of the above described known construction. 'In the energi-zin-g coil 41 of the et F the core 42 with the push-rod 43 is-jiigiipted to move vertically. The core rests normally on the abutment 44.. At its lower end it carries the insulated circuit closing member 45 of a thermostat controlling switch. Above the circuitclosing member 45 are fixed. at both sides of the core the contact springs 46, 46 in the insulating supports 47, 47". The release magnet F is constructed in a similar manner.

The release or tripping magnet also shows the connected with the conductor 2 is also protected against too high a starting current.

Upon engagement of the circuit-closing members 45 with the contact springs 46, of the respective tripping mechanisms, a thermostatic switch 0 is energized to open the circuit of the holding coil on'the'low-voltage relay to permit the actuation of its armature by its sprin 13.

The switc operates in the following manner: as long as the current in the conductor 1 does not exceed the normal service current, the core 42 rests upon the abutment orstop 44. If the motor current exceeds the normal service current without exceedin the normal starting current the core 42 is raised and closes by means of the circuit closing member 45 the contact springs 46, .46 of the thermostat becomes heated,-it opens its switch 40 by actuating the pivoted armature 39 against the force of the restraining spring38.

The thermostat E then interrupts the cir-. cuit of the coil 7 of the low voltagerel'ay G. The helical spring 13 now separates the armature 12from its magnet pole and the armature throws the loose push-rod 43 against the roller 21 of the switch. However when the normal starting cui'rent isexceeded in the conductor 1, the 'tractive power of the magnet F suflices to raise the core 1n opllO ' exceeds the service current, the core 42 in the magnet F is also raised and the thermostat switch is closed but the push-rod 43' remains upon the armature 12 of the lowvoltage relay. If the current increases the core is raised higher, strikes the collar 48 and carries the push-rod 43' along with it. The dimensions and the arrangement are such that the push-rod 43 here also moves the switch roller 21 upwards and trips the switch.

What I claim is In an automatic switch of the class described, tripping mechanism, an electromagnet arranged to operate said tripping mechanism upon heavy overloads, contact members associated with said electromagnet, means including said electromagnet for operating said contact members at a lower current value than that. required to operate the tripping mechanism, comprising a retarded relay connected to said contact members and a lowvoltage magnet operated by said retarded relay and operative to control said tripping mechanism.

In testimony whereof I affix my signature.

GOTTLIEB SPEISER. 

